2455-14-3Relevant articles and documents
Oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen in the absence of base catalysts
Bukharov,Fazlieva,Mukmeneva,Akhmadullin,Morozov
, p. 1805 - 1807 (2002)
Use of dimethylformamide as solvent and preliminary addition of 3,5,3′,5′-tetra-tert-butyl-4,4′-diphenoquinone allow oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen to be efficiently performed in the absence of base catalysts.
Selective Electrochemical versus Chemical Oxidation of Bulky Phenol
Zabik, Nicole L.,Virca, Carolyn N.,McCormick, Theresa M.,Martic-Milne, Sanela
, p. 8914 - 8924 (2016)
The electrochemical oxidation of selected tert-butylated phenols 2,6-di-tert-butyl-4-methylphenol (1), 2,6-di-tert-butylphenol (2), 2,4,6-tri-tert-butylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5) was studied in an aprotic environment using cyclic voltammetry, square-wave voltammetry, and UV-vis spectroscopy. All compounds exhibited irreversible oxidation of the corresponding phenol or phenolate ion. Compound 2 was selectively electrochemically oxidized, while other phenol analogues underwent mostly chemical oxidation. The electrochemical oxidation of 2 produced a highly absorbing product, 3,5,3′,5′-tetra-tert-butyl-4,4′-diphenoquinone, which was characterized by X-ray crystal diffraction. The electrochemical oxidation was monitored as a function of electrochemical parameters and concentration. Experimental and theoretical data indicated that the steric hindrance, phenoxyl radical stability, and hydrogen bonding influenced the outcome of the electrochemical oxidation. The absence of the substituent at the para position and the presence of the bulky substituents at ortho positions were structural and electrostatic requirements for the selective electrochemical oxidation.
Enantioselective Desymmetrization of 1,4-Dihydropyridines by Oxidative NHC Catalysis
Di Carmine, Graziano,Ragno, Daniele,Brandolese, Arianna,Bortolini, Olga,Pecorari, Daniel,Sabuzi, Federica,Mazzanti, Andrea,Massi, Alessandro
, p. 7469 - 7474 (2019)
The unprecedented desymmetrization of prochiral dialdehydes catalyzed by N-heterocyclic carbenes under oxidative conditions was applied to the highly enantioselective synthesis of 1,4-dihydropyridines (DHPs) starting from 3,5-dicarbaldehyde substrates. Synthetic elaboration of the resulting 5-formyl-1,4-DHP-3-carboxylates allowed for access to the class of pharmaceutically relevant 1,4-DHP-3,5-dicarboxylates (Hantzsch esters). DFT calculations suggested that the enantioselectivity of the process is determined by the transition state involving the oxidation of the Breslow intermediate by the external quinone oxidant.
Solvent-free oxidative coupling of 2-naphthols catalyzed by hydrotalcite-like compounds in aerobic conditions
Sugamoto, Kazuhiro,Matsushita, Yoh-Ichi,Matsui, Takanao
, p. 263 - 266 (2012)
Abstract: The hydrotalcite-like compound having ruthenium ions, cobalt ions, and iron ions in the Brucite layer and CO3 anions in the interlayer (Ru-Co-Fe-CO3 HTLC) was found to be effective heterogeneous catalyst for the solvent-free oxidative coupling of 2-naphthols in aerobic conditions. The catalyst could be easily recovered and reused repeatedly for the reaction.
Spectrophotometric determination of formation constants for the Cu-ethylenediamine-halogen (chloride and bromide) system and their catalytic effect on the oxidative coupling of 2,6-di-tert-butyl-phenol
Segoviano-Garfias, José J.N.,Moreno-Esparza, Rafael,Mendoza-Díaz, Guillermo
, p. 3461 - 3468 (2010)
In order to explain the mechanism of the dimerization of 2,6-di-tert-butyl-phenol when catalyzed by the copper-ethylenediamine complexes, a spectrophotometric study of the speciation of copper(II) complexes in methanol of Cu(II), ethylendiamine and Cl- or Br- was carried out at 303 K. The formation constants obtained for the copper chloride system are: log β101 = 2.90 ± 0.03, log β102 = 6.39 ± 0.03 and log β103 = 8.62 ± 0.04, for the copper bromide system are log β101 = 3.01 ± 0.10, log β102 = 5.50 ± 0.08, for the copper-ethylendiamine complexes are log β110 = 6.13 ± 0.05 and log β120 = 10.54 ± 0.08, and for the ternary copper-ethylenediamine chloride or bromide systems are log β111 = 10.21 ± 0.03 and log β111 = 10.07 ± 0.03, respectively. Knowing the speciation of the copper-ethylenediamine-halide systems, the kinetic studies can be correlated with the species in solution. Comparative studies of the oxidation reaction of 2,6-di-tert-butyl-phenol using different copper(II) complexes with chloride or bromide and ethylenediamine as catalyst are reported. Their catalytic activity in the oxidation of 2,6-di-tert-butyl-phenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm ( = 3.95 × 104 mol-1 L cm-1 at 303 K). The results indicate that the most active species are [Cu(en)X]+, where X is bromide or chloride, Both complexes have similar activity.
Singlet Character of Coordinatively Bound Oxygen, II
Duchstein, Hans-Juergen
, p. 460 - 464 (1987)
The oxygenation of 1,5-dihydroxynaphthalene (1) and 2,6-di-t-butylphenol (4) with Co-salen as a catalyst has been examined.The activation of oxygen in these reactions is different.From reactions with specific quenchers and the measurement of ultraweak chemiluminescence it is concluded that, depending on the nature of the substrate, Co-salen activates oxygen in the singlet state or in the radical state.This behavior must be considered when cobalt complexes are investigated as model substances of enzymatic oxygenation reactions.
EPR-spectroscopic Experiments with the Co-Salen/O2-Complex, VI: Differentiation of the Bound Oxygen
Duchstein, Hans-Juergen,Baumgarten, Martin
, p. 781 - 785 (1988)
EPR-spectroscopic experiments of Co-Salen depending on solvent, substrate and oxygen are described.We explain the EPR-inactivity in acetonitrile with a Co-salen-dimer.Co-Salen, depending on the nature of the substrate, is able to activate oxygen into different species, which allow 1. (4+2)-cycloadditions very similar to the reactions with singlet oxygen in the case of 1,5-dihydroxy-naphthalene (1) and 2. radical-reactions with 2,6-di-t-butylphenol (4).These experiments are consistent with former chemiluminescence measurements.We describe an activation model of Co-salen/02 with the investigated reactions.
Structural characterization and electrochemical properties of the 3,3′-5,5′-tetra-tert-butyl-4,4′-diphenoquinone
Tuemer, Mehmet,Aslantas, Mehmet,Sahin, Ertan,Deligoenuel, Nihal
, p. 477 - 481 (2008)
Crystals of the 3,3′-5,5′-tetra-tert-butyl-4,4′-diphenoquinone (TTBDQ) in the reaction mixture DCM/MeOH (1:1, v/v) were obtained as a result of C{single bond}C coupling reaction of the sterically hindered phenol (2,6-di-tert-butylphenol, DTBP) using the binuclear Co(II) complexes. The oxidation product (TTBDQ), C28H40O2, crystallizes in the space group P over(1, ) with one-half molecule in the asymmetric unit and the other half generated by an inversion centre. The diphenoquinone moiety is planar within ±0.016(3) A. The crystal structure is stabilized by intramolecular C{single bond}H...O hydrogen bonds. The spectroscopic and electrochemical properties of the TTBDQ also have been studied.
Physical and Chemical Properties of Mononuclear Cobalt Dioxygen Complexes with Tetraimidazolyl-Substituted Pyridine Chelates
Tamagaki, Seizo,Kanamaru, Yutaka,Ueno, Masanori,Tagaki, Waichiro
, p. 165 - 174 (1991)
A new class of mononuclear superoxocobalt complexes containing four equal imidazolyl-donors and one pyridyl-donor per cobalt(II) ion was prepared and their chemical and physical properties were compared with those of cobalt(II) Schiff-base type dioxygen complexes.
Carboxamidate Ligand Noninnocence in Proton Coupled Electron Transfer
McManus, Caitilín,Mondal, Prasenjit,Lovisari, Marta,Twamley, Brendan,McDonald, Aidan R.
, p. 4515 - 4523 (2019)
Recent breakthroughs have brought into question the innocence (or not) of carboxamidate donor ligands in the reactivity of high-valent oxidants. To test the reactivity properties of high-valent carboxamidate complexes, [NiII(tBu-terpy)(L)] (1, tBu-terpy = 4,4′,4′′-tri-tert-butyl-2,2′6′,2″-terpyridine; L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate) was prepared and converted to [NiIII(tBu-terpy)(L)]+ (2) using ceric ammonium nitrate. 2 was characterized using electronic absorption and electron paramagnetic resonance spectroscopies and electrospray ionization mass spectrometry. 2 was found to be a capable oxidant of phenols and through kinetic analysis was found to oxidize these substrates via a nonconcerted or partially concerted proton coupled electron transfer (PCET) mechanism. The products of PCET oxidation of phenols by 2 were phenoxyl radical and the protonated form of 1, 1H+. 1H+ was crystallographically characterized providing convincing evidence of 1's ability to act as a proton acceptor. We demonstrate that the complex remained intact through a full cycle of oxidation of 1 to 2, PCET of 2 to yield 1H+, and deprotonation of 1H+ to yield 1 followed by reoxidation of 1 to yield 2. The N-H bond dissociation energy of the protonated amide in 1H+ was determined to be 84 kcal/mol. Our findings illuminate the role carboxamidate ligands can play in PCET oxidation.
